ASU focuses on herbicide symptomology

The large grid of herbicide research plots across the highway from the Arkansas State University campus isn’t always clean and pretty. But aesthetics don’t matter in this outdoor classroom, say the Arkansas Extension researchers running the Jonesboro, Ark.-based program. All that matters is that visitors leave with a fuller grasp of herbicide symptomology.

“We’ve been at this for a long time,” says Cal Shumway, ASU associate professor of agronomy who has overseen the operation since its inception 11 years ago. “This started as a training opportunity only for employees of the Arkansas State Plant Board, a way of ensuring they understood herbicide symptomology.”

Originally, the training lasted for only one day. Then, the Arkansas Crop Protection Association thought the plot work would help fulfill its educational mission. With such backing, the research work has grown from the original 30 plots to the current 140-plus.

“(The ACPA) has really supported our work and we’ve opened the training up to the public. Many consultants, Extension agents, chemical and seed companies all take advantage of it.”

The effectiveness as a teaching tool begins to fade after a few weeks. While viable, tours and classes visit frequently.

“We leave out plot plans (through early July). After a couple of weeks, the plots begin to lose their impact. Non-lethal dosages — like on the yard plots — grow out of any damage. And any susceptible crops are probably dead by then. But the public is welcome at anytime.”

The researchers try to get new chemistries into the plot mix as soon as possible. When a new herbicide comes in — whether fully labeled or a Section 18 — “we put it in immediately,” says Shumway. “We usually don’t go with numbered compounds but as soon as they’re registered, they’re added.”

Researchers from across the Mid-South visit the plots. This year, even a team from New Mexico made the trip.

“Representatives from the Arkansas Highway Department have come in the last couple of years. You’ll see the department employees spraying a lot of medians, roadsides and whatnot to keep weeds down. So they’re interested in what we’re doing. The plots really do provide answers and examples for a lot of different jobs.”

In the project’s early days the plots’ purpose was to ensure Plant Board inspectors were using similar terminology. One man’s “yellowing” is another man’s “chlorosis.”

“What can happen is a mix of confusing terminology that’s not terribly enlightening. A term used in the coffee shop to describe something doesn’t always translate well in a written report.

“An example would be the phrase ‘burnt leaves.’ That’s very general and, depending on the situation, ‘necrosis’ or ‘desiccation’ would be better. Even though most producers would know what was being talked about, it’s better to be more precise.”

That’s especially true since the Plant Board inspectors so often deal with drift incidents.

“We had a bit of Newpath and glyphosate drift earlier this year,” said Bob Scott, Arkansas Extension weed specialist, who spoke at the June 22 field day at the plots. “Thankfully, it hasn’t been nearly as bad as it was last season. I don’t know if we’re doing everything right or if the wind hasn’t been blowing as hard. Maybe both. Regardless, we haven’t had as many concerns.”

Scott, who has also worked on the ASU plots from the beginning, said DD-50s are a little behind on rice this year. Much of the crop has “moved into green-ring, quarter-inch/half-inch internodes.

“That means we really need to be careful about spraying Roundup around rice. Rice is sensitive at two-leaf to three-leaf stage. Then, while tillering and pre-flood/early-post, it gets sort of bullet-proof.”

But once the crop hits green-ring — “and really anytime from then until panicle emergence and development” — glyphosate drift can damage seedheads. And there may be no symptomology until the heads emerge.

“As you’re out driving around, you’ll see growers with late beans and second applications going out,” said Scott. “Be diplomatic but, if possible, make sure everyone understands how sensitive to drift rice is right now.”

With the inspector program a success, the researchers wondered if others would find the plots useful.

“So much work goes into putting this together, we decided we should maximize the resource. For the last eight years, or so, the plots have been open to the public.”

The plots typically feature a wide range of spray dates so visitors will see herbicide symptomology in various stages.

“This year, we also have soil-applied,” says Scott. “There’s been more interest in those. There are over 20 plots out there with only one early-post product.

“We had been doing the soil-applied plots every two or three years. That was done when there was a little bit of a transition away from soil-applied to more foliar applications in Roundup Ready and Clearfield crops. Obviously, that technology placed more emphasis on foliar-applied products.”

With the possibility of soil-applied products being used as a resistance management tool, “we added around 25 soil-applied plots this year. And that may be expanded in 2008.”

There are also plots representing standard yards (mostly bermudagrass with perennial flowers), gardens and trees that are sprayed with chemicals the Plant Board receives the most complaints on. “It isn’t the ‘Dirty Dozen,’” says Shumway. “More like the ‘Dirty Six or Seven.’

“Recently, we’ve expanded the number of plant types in the program. We’ve always had a few garden crops. But lately, we’ve tried to include all major garden crops to see the different modes of action.”

Shumway and Scott try to get at least a couple of planting dates in the plots. The type of chemistry determines when a herbicide is applied.

“Something that’s fast-acting like paraquat — spray it in the morning and there are symptoms two hours later — will be applied one or two days before the tours. For ALS-inhibitors, we apply four or five days prior.”

The researchers are trying to develop symptomology at different stages of a crop’s development.

Towards that goal, “we spread out the spray dates. Again, when an inspector gets a call, the application could have come just days after application or, it could be two weeks. So we want them to have examples of both. Some materials go out with a single application in the crop section. Others go out with two applications.”

A Web site documenting the symptomology plots has been up since Jan. 3.

“Right now, we have 1,200 images that can be downloaded for study. Those are good-sized and high clarity. We didn’t cut back on the size because everyone needs to see the symptoms clearly.”

Shumway, who says the EPA was very helpful in getting the site running, promises new images will be added regularly. “In the last week, I’ve had 27 rolls of film developed. Those photos will be added to the site in a couple of months. Also on the site are several presentations open for downloading. Those are public domain and hold good information. The site even has a 44-page manual that folks can access.”

More than herbicides cause crop damage, says Shumway. “Maybe we’ll want to add diseases that mimic herbicide injury. Maybe we can look at certain nutrient deficiencies or toxicities that may produce herbicide-type symptomology. That’s where the operation is weakest. Hopefully, we’ll be able to fix that soon.”